Metering and mixing devices which operate at either low pressure or high pressure have been known for some time. Some devices of this type allow the metering rate to be altered in a controlled manner for one or more reactants during the metering process. In this process, for example, the stoichiometric ratio is changed (or one reactant is exchanged continuously for another) in order to produce zones having differing properties in the resulting shaped articles. With a low pressure metering device which is provided with a stirrer, all reactants are introduced into the large-volume stirrer mixing chamber and mixed therein in one stage. Premixing of reactants in a preselected, exact metering ratio to form a multi-component reaction mixture and subsequent mixing (which is controlled relative to the metering ratio) with at least one second, pre-mixed multi-component reaction mixture, which is metered in the stoichiometrically correct ratio is not possible. In addition, low pressure stirrer mixers can be used for the intermittent production of, for example, solid, bubble-free shaped articles only when using relatively slowly reacting mixtures which do not require rinsing or cleaning of the mixing chamber between two mold filling operations. If it is necessary to rinse or clean the mixing chamber, the air present in the large-volume mixing chamber is introduced into the reaction mixture at the beginning of each mixing operation. This results in bubbles and a partially foamy structure, at least at the beginning of each filling operation, which make the shaped article unservicable. Another disadvantage lies in the sealing of the stirrer shaft which is sensitive to leakages and to pressure.
The high pressure metering devices which are commercially available at present allow the metering rate of individual reactants to be changed relative to each other. They also allow a continuous synchronous change in the metering rate of several reactants at a constant metering ratio. The associated injection mixheads which are currently used have their injection and mixing conditions adapted to a substantially constant metering rate and to a substantially constant viscosity of the reactants due to the preselection and tight adjustments of the cross-sections of the injection nozzles. As a result, a marked reduction in the metering rate of one reactant with a constant nozzle cross-section at the mixing chamber inlet, inevitably leads to a corresponding drop in the metering pressure and thus in the mixing power. The mixing of the reactants in the injection chamber is no longer satisfactory.
Injection mixers having self-cleaning design, in conjunction with high pressure metering devices, are known to have numerous advantages over low pressure devices. For example, highly reactive systems having setting times as low as one second can be processed. Additionally, it is not necessary to rinse the mixing chamber. The volume of the mixing chamber can be kept extremely small at a few cubic centimeters and solid, substantially bubble-free reaction mixtures can be consequently produced, if necessary, from the beginning of the operation to the end. It is also possible to mix up to 6 reactants in one mixhead under the substantially constant metering conditions described above. However, if these conditions are to be changed during the mixing operation, the results are unsatisfactory.
The object of the invention is to propose a method and a device for the production of polymeric shaped articles from multi-component reaction materials such as those for forming, for example, polyurethane, epoxy resin, polyester resin or polyamide shaped articles wherein flowable reactants (which, if necessary, can be metered by means of high pressure pumps and which optionally contain fillers as well as optionally flowable additives), are mixed together in such a way that it is possible to significantly influence the metering and mixing operations.